The present invention relates to a method for synthesizing complexes of platinum with iminoethers and to their use as antitumoral drugs and nucleotide-base modifiers.
Specifically, the present invention relates to a method for synthesizing complexes of platinum(II) with iminoethers and to their use both as broad-spectrum antitumoral drugs and as nucleotide-base modifiers in antisense and/or antigene oligonucleotides.
The inorganic compound cis-diaminodichloroplatinum(II) (cis-[PtCl2(NH3)2], cis DDP, also commonly known as cisplatinum, is a molecule having an antitumoral action which has been widely used clinically, particularly for treating solid tumors.
The chemotherapeutic effect of cisplatinum arises from a biochemical mechanism which is still not entirely known and which, since the drug interacts with cell DNA, forming intra- and interstrand bifunctional adducts, is probably due to structural and functional changes associated with the formation of adducts, particularly intrastrand adducts between adjacent purines. On the basis of current knowledge, however, a significant contribution to the action of cisplatinum by adducts of the interstrand type cannot be ruled out.
It is known that initial structure-activity correlation studies concerning with platinum complexes having the general formula [PtnX2A2], where X is a leaving anionic group and A2 are two monodentate amine ligands or a bidentate amine ligand, demonstrated that the compounds having an antitumoral activity had their X groups in a cis configuration and vice versa that the geometric isomer of cisplatinum, trans-[PtCl2(NH3)2], trans-DDP, like other platinum complexes having X-group in trans geometry, had no antitumoral activity. Accordingly, in the past the search for cisplatinum derivatives characterized by lower systemic toxicity and by a different spectrum of activity was orientated almost exclusively toward cis-geometry compounds.
However, platinum complexes with a trans geometry of the leaving ligands have been recently identified which are characterized by antitumoral properties which have been verified in experimental systems in vitro and/or in vivo. In particular, the following are known among these complexes:
complexes having the general formula trans-[PtCl2(L)(Lxe2x80x2)], where L, Lxe2x80x2 is pyridine, thiazole, quinoline. These compounds, particularly with reference to trans-[PtCl2(pyridine)2], have been shown to have a higher cytotoxic effect in vitro against tumor cells than trans-DDP;
complexes of platinum with iminoethers, with particular reference to the complex trans-[PtCl2{E-HNxe2x95x90C(OMe)Me}2], where E is the configuration of the iminoether group, indicating that the platinum and the methoxyl are in the trans position with respect to the Cxe2x95x90N double bond. This complex has a cytotoxic in vitro effectiveness similar to that of cisplatinum and an antitumoral activity in vivo with respect to solid and lymphoproliferative murine tumors.
complexes of platinum(IV), with particular reference to an octahedral compound of platinum(IV) with trans geometry and having the formula trans-[PtCl2(OH)2(NH3){NH2(C6H11)}] and analogs thereof, have shown antitumoral activity in vitro and in vivo.
Recently it has been found that known antitumoral platinum complexes having a trans geometry have an activity against cisplatinum-resistant tumor cells, thus providing new guidelines for research into platinum complexes having a different mechanism of action with respect to cisplatinum.
Biomedical technology currently uses synthetic oligonucleotides in order to achieve selective inhibition of gene expression for the analysis of specific genetic functions and for the possible pharmacological treatment of diseases caused by alterations of cell gene expression.
These synthetic oligonucleotides are known to be an elective class of drugs for regulating mRNA translation and DNA transcription, in antisense and antigene therapeutic strategies, respectively.
In order to improve the biological effectiveness of synthetic oligonucleotides, providing a stable and irreversible interaction with the target sequences, some chemical functional groups and/or photonically activated agents have been conjugated with synthetic oligonucleotides.
However, this model has been found to have drawbacks, mainly due, in the case of the presence of chemical functional groups, to the onset of non-sequence-specific association reactions, and due, in the case of the presence of photonically activated agents, to difficulty in application in in vivo systems.
A general aim of the present invention is to avoid or significantly reduce the disadvantages noted in the known art.
A primary object of the present invention is to provide new broad-spectrum antitumoral drugs whose administration entails reduced side effects.
Another object of the present invention is to provide platinum(II) complexes which can be used as agents for modifying nucleotide bases in antisense and/or antigene oligonucleotides which are highly specific and do not entail high production costs.
Another object is to provide a method for synthesizing complexes of platinum with iminoethers which is simple to perform.
In view of this aim, these objects and others which will become apparent hereinafter, according to the present invention, complexes of platinum(II) with iminoethers are provided, said complexes having the formula (I):
[Pt11X2(L)(Lxe2x80x2)]xe2x80x83xe2x80x83(I),
wherein
X is a monoanionic ligand, preferably a halide, more preferably selected from Clxe2x88x92 and Ixe2x88x92;
L is an iminoether group or ligand, preferably having the formula HNxe2x95x90C(ORxe2x80x2)R, or the formula Nxe2x95x90C(ORxe2x80x2)xe2x80x94(CH2)nxe2x80x94CH2, or the formula Nxe2x95x90C(R)xe2x80x94Oxe2x80x94(CH2)nxe2x80x94CH2, wherein
R and Rxe2x80x2 are a linear or branched alkyl, preferably a lower alkyl, more preferably an alkyl containing 1 to 6 atoms of C or an aryl, said aryl preferably being a substituted or unsubstituted phenyl-group and
nxe2x95x901, 2, 3;
Lxe2x80x2 is an amine group or ligand or, exclusively for the case of cyclic iminoethers, a second iminoether group.
Advantageously, said amine group is selected from ammonia, a primary or secondary aliphatic amine or an aromatic amine, such as piridine or quinoline, optionally substituted.
Platinum(II) complexes having the formula (I) according to the present invention can have a cis or trans geometry of the monoanionic ligands and of the aminic and iminoether ligands, with respect to the metallic center; moreover, the iminoether ligand HNxe2x95x90C(ORxe2x80x2)R can have a different configuration (E or Z) according to the relative position (trans or cis) of the ORxe2x80x2 group and of the metallic center with respect to the Cxe2x95x90N double bond.
According to one embodiment of the present invention, said platinum(II) complexes have the following structure forms: 
According to another aspect of the present invention, a process is provided for synthesizing compounds of platinum(II) with iminoethers having the formula [Pt11X2(L)(Lxe2x80x2)], wherein
X is a monoanionic ligand, preferably a halide, more preferably selected from Clxe2x88x92 and Ixe2x88x92;
L is an iminoether group or ligand having the formula HNxe2x95x90C(ORxe2x80x2)R or the formula 
or the formula 
where R and Rxe2x80x2 are an alkyl or an aryl and n=1, 2, 3;
Lxe2x80x2 is an amine group or ligand or, exclusively for the case of cyclic iminoethers, a second iminoether group; said process comprising the steps of:
1) treatment of cis-[PtX2(Lxe2x80x2)2] in a mixture of water and nitrile (NCR) in order to obtain trans-[PtX2(Lxe2x80x2)(NCR)];
2) treatment of trans-[PtX2(Lxe2x80x2)(NCR)] with an alcohol and a base (a hydroxide of an alkaline/alkaline-earth metal) to produce trans-[PtX2(Lxe2x80x2) (Z-L)];
3) transformation of the trans-[PtX2(Lxe2x80x2)(Z-L)] into the isomer trans-[PtX2(Lxe2x80x2)(E-L)] by reaction with a hydroxide of an alkaline/alkaline-earth metal in an alcohol;
4) in the case of cyclic iminoethers, the acyclic species initially formed [HNxe2x95x90C(Oxe2x80x94(CH2)nCH2X)R] or [HNxe2x95x90C(OR)xe2x80x94(CH2)nCH2X] is subjected to a cyclization reaction in a basic environment, with elimination of HX and formation of 
and 
respectively;
5) reaction sequences 2, 3, 4 can be applied to the [PtX2(NCR)2] substrates in order to obtain the platinum(II) compounds with two anionic ligands (X) and two cyclic iminoether groups.
According to another aspect, the present invention relates to complexes of platinum(II) with iminoethers having the formula (I) for use as a medicament and/or to the use thereof for the manufacture of a medicament for treating tumours.
In particular, it has been verified that complexes of platinum(II) with iminoethers having the formula (I) have a marked antitumoral activity which has been confirmed in experimental systems in vitro and in vivo. In particular, the platinum complexes according to the invention have a broad antitumoral spectrum accompanied by reduced onset of side effects.
According to another aspect, the present invention relates to the use of complexes of platinum(II) with iminoethers having the formula (I) as agents for modifying the nucleotide bases into antisense and/or antigene oligonucleotides.
In particular, it has been found that the specific properties of interaction with DNA of the [Pt11X2(L)(Lxe2x80x2)] complexes with trans geometry of the L, Lxe2x80x2 ligands described above give antisense and/or antigene oligonucleotides, appropriately modified with the platinum complex, the ability to irreversibly bind to the complementary sequences of nucleic acids, thus being able to determine the inhibition of RNA translation and/or gene transcription.
The above complexes having the formula trans-[Pt11X2(L)(Lxe2x80x2)], owing to their specific structure and chemical reactivity, can be used to selectively modify one of the nucleotide bases of an antisense and/or antigene oligonucleotide. In both cases, the platinum complex forms a stable adduct of the monofunctional type which rapidly becomes an intercatenary bifunctional adduct when the modified oligonucleotide associates with its complementary nucleic acid sequence.